June 18, 2018
You must eat me to thrive.
What molecule am I?
Image of L-Threonine 3D Image of L-Threonine

L-Threonine is an essential amino acid, that is, humans must obtain it from foods because their bodies cannot synthesize it. Foods that contain high amounts of protein, such as meats, fish, eggs, and dairy products, are good sources of L-threonine.

L-Threonine, abbreviated Thr, is the last common amino acid to be discovered. Although biochemist William C. Rose and colleagues at the University of Illinois (Urbana–Champaign) are usually credited with discovering Thr in 1936, biochemist Samuel B. Schryver and botanist H. W. Buston at Imperial College London reported isolating it from oat protein in 1926.

Threonine has two chiral centers and therefore four possible stereoisomers. The isomers other than Thr (D-, L-allo-, and D-allo-threonine) are rare in nature and have no value, nutritional or otherwise.

These days, most Thr is synthesized rather than being obtained from natural proteins. But this past April, Evonik Industries (Essen, Germany) feeling competitive pressure, closed its L-threonine plant in Kaba, Hungary, causing ≈120 people to lose their jobs.


L-Threonine hazard information

GHS classification**: not a hazardous substance

**Globally Harmonized System of Classification and Labeling of Chemicals. 

L-Threonine fast facts

CAS Reg. No.72-19-5
Molar mass119.12 g/mol
Empirical formulaC4H9NO3
AppearanceColorless crystals
Melting point228–270 ºC (dec.)*
Water solubility97 g/L

*Depending on conditions.

Chemical Abstract Service - a division of ACS

Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.

Molecule of the Week needs your suggestions!

If your favorite molecule is not in our archive, please send us a message. The molecule can be notable for its current or historical importance or for any quirky reason. Thank you!

Stay Ahead of the Chemistry Curve

Learn how ACS can help you stay ahead in the world of chemistry.